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  • 1
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    Status of turbulence modeling for hypersonic propulsion flowpaths (2014)
    Springer
    Details
    Publication Date: 2014-01-16
    Print ISSN: 0935-4964
    Electronic ISSN: 1432-2250
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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    PAPER CURRENT
  • 2
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    On the use of optimization techniques for turbulence model calibration (2021)
    Elsevier
    Details
    Publication Date: 2021-01-01
    Print ISSN: 0045-7930
    Electronic ISSN: 1879-0747
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Published by Elsevier
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  • 3
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    Sidewall Effects on Exact Reynolds-Stress Budgets in an Impinging Shock Wave/Boundary Layer Interaction (2019)
    In:  CASI
    Details
    Publication Date: 2019-05-07
    Description: Large-eddy simulations are performed using wall-resolved mesh for a Mach 2.29 impinging shock wave/boundary-layer interaction. Flow conditions are based on an experiment and therefore entire span was simulated, including the two sidewalls. Mean flow comparison with the experimental data showed that the predicted interaction length was larger in the simulation. Time-series analysis of a rake of pressure signals immediately downstream of the mean reflected shock position showed a peak in weighted power spectral density occurred about St(sub Lint) = 0.01, owing to a larger interaction length. Budgets of Reynolds-stress transport calculated across the span and along the corner bisector showed high degree of anisotropy. Merging of the secondary flows and separation along the corner gave rise to unstable counter-rotating vortices, which straddle the corner and grow in size. This also leads to a development of new behavior in the viscous sublayer along the corner bisector, where the pressure strain and molecular diffusion mechanisms become prominent.
    Keywords: Aeronautics (General)
    Type: GRC-E-DAA-TN64126 , AIAA Science and Technology Forum and Exposition (SciTech); 7-11 Jan. 2019; San Diego, CA; United States
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  • 4
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    On the Use of Optimization Techniques for Turbulence Model Calibration (2019)
    In:  CASI
    Details
    Publication Date: 2019-05-24
    Description: This article discusses the use of numerical optimization procedures to aid in the calibration of turbulence model coefficients. Such methods would increase the rigor and repeatability of the calibration procedure by requiring clearly defined and objective optimization metrics, and could be used to identify unique combinations of coefficient values for specific flow problems. The approach is applied to the re-calibration of an explicit algebraic Reynolds stress model for the incompressible planar mixing layer using the Nelder-Mead simplex algorithm and a micro-genetic algorithm with minimally imposed constraints. Three composite fitness functions, each based upon the error in the mixing layer growth rate and the normal and shear components of the Reynolds stresses, are investigated. The results demonstrate a significant improvement in the target objectives through the adjustment of three pressure-strain coefficients. Adjustments of additional coefficients provide little further benefit. Issues regarding the effectiveness of the fitness functions and the efficiency of the optimization algorithms are also discussed.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: NASA/TM-2019-220163 , E-19680 , GRC-E-DAA-TN65018
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  • 5
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    Sidewall Effects on Exact Reynolds-Stress Budgets in an Impinging Shock Wave/Boundary Layer Interaction (2019)
    In:  CASI
    Details
    Publication Date: 2019-06-08
    Description: Large-eddy simulations are performed using wall-resolved mesh for a Mach 2.29 impinging shock wave/boundary-layer interaction. Flow conditions are based on an experiment and therefore entire span was simulated, including the two sidewalls. Mean flow comparison with the experimental data showed that the interaction was larger in the simulation. Time-series analysis of a rake of pressure probes immediately downstream of the mean reflected shock position showed a peak in weighted power spectral density occurred about $St_{Lint}=0.01$, owing to a larger interaction length. Budgets of Reynolds-stress transport calculated across the span and along the corner bisector showed high degree of anisotropy. Merging of the secondary flows and separation along the corner gives rise to unstablecounter rotating vortices, which straddle the corner and grow in size. This also leads to a development of new behavior in the viscous sublayer along the corner bisector, where the pressure strain andmolecular diffusion mechanisms become prominent.
    Keywords: Aeronautics (General)
    Type: NASA/TM-2019-220143 , E-19664 , AIAA–2019–1890 , GRC-E-DAA-TN65531
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  • 6
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    Use of Navier-Stokes methods for the calculation of high-speed nozzle flow fields (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Flows through three reference nozzles have been calculated to determine the capabilities and limitations of the widely used Navier-Stokes solver, PARC. The nozzles examined have similar dominant flow characteristics as those considered for supersonic transport programs. Flows from an inverted velocity profile (IVP) nozzle, an under expanded nozzle, and an ejector nozzle were examined. PARC calculations were obtained with its standard algebraic turbulence model, Thomas, and the two-equation turbulence model, Chien k-epsilon. The Thomas model was run with the default coefficient of mixing set at both 0.09 and a larger value of 0.13 to improve the mixing prediction. Calculations using the default value substantially underpredicted the mixing for all three flows. The calculations obtained with the higher mixing coefficient better predicted mixing in the IVP and underexpanded nozzle flows but adversely affected PARC's convergence characteristics for the IVP nozzle case. The ejector nozzle case did not converge with the Thomas model and the higher mixing coefficient. The Chien k-epsilon results were in better agreement with the experimental data overall than were those of the Thomas run with the default mixing coefficient, but the default boundary conditions for k and epsilon underestimated the levels of mixing near the nozzle exits.
    Keywords: AERODYNAMICS
    Type: NASA-TM-106551 , E-8703 , NAS 1.15:106551 , AIAA PAPER 94-3212 , Joint Propulsion Conference; Jun 27, 1994 - Jun 29, 1994; Indianapolis, IN; United States
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  • 7
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    Computational Study of Axisymmetric Off-Design Nozzle Flows (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Computational Fluid Dynamics (CFD) analyses of axisymmetric circular-arc boattail nozzles operating off-design at transonic Mach numbers have been completed. These computations span the very difficult transonic flight regime with shock-induced separations and strong adverse pressure gradients. External afterbody and internal nozzle pressure distributions computed with the Wind code are compared with experimental data. A range of turbulence models were examined, including the Explicit Algebraic Stress model. Computations have been completed at freestream Mach numbers of 0.9 and 1.2, and nozzle pressure ratios (NPR) of 4 and 6. Calculations completed with variable time-stepping (steady-state) did not converge to a true steady-state solution. Calculations obtained using constant timestepping (timeaccurate) indicate less variations in flow properties compared with steady-state solutions. This failure to converge to a steady-state solution was the result of using variable time-stepping with large-scale separations present in the flow. Nevertheless, time-averaged boattail surface pressure coefficient and internal nozzle pressures show reasonable agreement with experimental data. The SST turbulence model demonstrates the best overall agreement with experimental data.
    Keywords: Aerodynamics
    Type: NASA/TM-2003-212876 , E-14289 , AIAA Paper 2004-0530 , 42nd Aerospace Sciences Meeting and Exhibit; Jan 05, 2004 - Jan 08, 2004; Reno, NV; United States
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  • 8
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    Implementation of a two-equation k-omega turbulence model in NPARC (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The implementation of a two-equation k-omega turbulence model into the NPARC flow solver is described. Motivation for the selection of this model is given, major code modifications are outlined, new imputs to the code are described, and results are presented for several validation cases: an incompressible flow over a smooth flat plate, a subsonic diffuser flow, and a shock-induced separated flow. Comparison of results with the k-epsilon model indicate that the k-omega model predicts simple flows equally well whereas, for adverse pressure gradient flows, the k-omega model outperforms the other turbulence models in NPARC.
    Keywords: AERODYNAMICS
    Type: NASA-TM-107080 , NAS 1.15:107080 , E-9955 , AIAA PAPER 96-0383 , NIPS-96-08118 , Aerospace Sciences Meeting and Exhibit; Jan 15, 1996 - Jan 18, 1996; Reno, NV; United States
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  • 9
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    Comparison of Turbulent Thermal Diffusivity and Scalar Variance Models (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper will include a detailed comparison of heat transfer models that rely upon the thermal diffusivity. The goals are to inform users of the development history of the various models and the resulting differences in model formulations, as well as to evaluate the models on a variety of validation cases so that users might better understand which models are more broadly applicable.
    Keywords: Aerodynamics; Fluid Mechanics and Thermodynamics
    Type: GRC-E-DAA-TN28774 , AIAA SciTech Conference 2016; Jan 04, 2016 - Jan 08, 2016; San Diego, CA; United States
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  • 10
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    Wind-US Results for the AIAA 1st Propulsion Aerodynamics Workshop (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This presentation contains Wind-US results presented at the 1st Propulsion Aerodynamics Workshop. The The workshop was organized by the American Institute of Aeronautics and Astronautics, Air Breathing Propulsion Propulsion Systems Integration Technical Committee with the purpose of assessing the accuracy of computational computational fluid dynamics for air breathing propulsion applications. Attendees included representatives from representatives from government, industry, academia, and commercial software companies. Participants were were encouraged to explore and discuss all aspects of the simulation process including the effects of mesh type and mesh type and refinement, solver numerical schemes, and turbulence modeling. The first set of challenge cases involved computing the thrust and discharge coefficients for a series of convergent convergent nozzles for a range of nozzle pressure ratios between 1.4 and 7.0. These configurations included a included a reference axisymmetric nozzle as well as 15deg , 25deg , and 40deg conical nozzles. Participants were also asked also asked to examine the plume shock structure for two cases where the 25deg conical nozzle was bifurcated by a bifurcated by a solid plate. The final test case was a serpentine inlet diffuser with an outlet to inlet area ratio of 1.52 ratio of 1.52 and an offset of 1.34 times the inlet diameter. Boundary layer profiles, wall static pressure, and total and total pressure at downstream rake locations were examined.
    Keywords: Aerodynamics
    Type: E-18411 , AIAA 1st Propulsion Aerodynamics Workshop; Jul 29, 2012; Atlanta, GA; United States
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